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    <title>Document</title>
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<body>
    <script>
 //1.       
          function A() { }
                A.prototype.n = 1
                var b = new A()
                A.prototype = {
                    n: 2,
                    m: 3,
                }
                var c = new A()
                console.log(b.n, b.m, c.n, c.m);//1 undefined  2 3
 //2.       
        function Foo() {
                Object.prototype.a = function () {
                    console.log('可访问a')
                }
            }
             Function.prototype.b = function () {
                console.log('可访问b')
            }
            var foo = new Foo()
            foo.a();// 可访问a
            //foo.b();//报错
            Foo.a();//可访问a
            Foo.b();//可访问b

    </script>
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